Geochemical Characteristics of Strongly Acidic Thermal Water of the Tamagawa Hot Spring in North-Eastern Japan--Implications for Source and Transportation of Rare Metals in Magmatic Hydrothermal to Geothermal Systems

摘要

The Tamagawa Hot Spring, from which Ra-Pb-Sr-bearing barite precipitates, is a representative hot spring in a volcanic gas-bearing hydrothermal system associated with Quaternary andesitic to dacitic magmatic activity beneath the Yakeyama Volcano. Thermal water in the Tamagawa Hot Spring is divided into three types: Cl-SO_4-type (Ohbuki hot spring: pH 1.2); SO_4-type (pH 1.8 to 2.9); and neutral-type (pH 6.1). The concentrations of dissolved components in the Ohbuki Cl-SO_4-type thermal water are about ten times higher than in the SO_4-type thermal water. The ~(87)Sr/~(86)Sr isotopic signatures of the Ohbuki Cl-SO_4-type thermal waters (0.703992 +- 0.000004 to 0.704032 +- 0.000006) are different from those ofSO_4-type thermal waters (0.704245 +- 0.000003) formed by the interaction of andesitic volcanic rocks (0.704065 +- 0.000007 to 0.704093 +- 0.000009) and groundwater derived from river water (0.704314 +- 0.000012 to 0.704519 +- 0.000013) in a shallower part of the hot spring area. The possible origins of Sr in the Ohbuki Cl-SO_4-type thermal water and in the SO_4-type thermal water are different. The Sr isotopic ratios (0.704130 +-0.000012 to 0.707556 +- 0.000014) of Aniai Formation and PreYakeyama Lake deposits occurring below the hot spring area are distinctly higher than those of the Cl-SO_4-type thermal water.